InkThrift CL longevity and indoor lighting

This paper is intended to address InkThrift® CL ink longevity when displayed in various indoor lighting conditions. The other purpose of this paper is to give the reader an insight into deciding whether to use dye inks where one would normally use pigment ink is a good decision for the intended purpose.

Background

InkThrift CL is a new product from Vermont PhotoInkjet. It is a brand new formulation of dye ink which is designed for better longevity than InkThrift PRO inks. it is available for a wide range of Epson desktop printers. The 68, 77, and 79 range of EPSON printers use a very long lasting dye ink called Claria® that is compatible on both matte and glossy papers. But, these printers use tiny and expensive one time use cartridges that contribute to significant amounts of eco-waste. The amount of single use cartridges that are thrown away into landfills is staggering. Some estimates have it at more than 450 million carts a year in the USA alone. InkjetMall’s new EasyFill® system for Epson Claria printers combines easily replaceable ink capsules with keys that are inserted into the printer where cartridges are normally installed.

Many indoor locations are unsafe for dye inks

Kodak indicates that 120 Lux is the limit of safe display conditions for dye color photographs and that 90% of all color photographs are displayed in 120 Lux or less. Wilhelm indicates that 450 Lux is the limit of safe display conditions for color pigment photographs. An interior room in a house lit indirectly by incandescent light is considered to be 120 Lux. Museums are limited to 50 Lux (for comparison). Bright offices are about 450 Lux but often much brighter. A print displayed at 450 Lux has only 25% of the longevity it would have if it were displayed at 120 Lux. A print displayed at 5000 Lux would have less than 3% of the longevity it would have had it been displayed at 120 Lux.

A good perspective to keep in mind in comparing dye inks to pigment inks is that it would take years to damage a pigment print displayed in an unsafe condition, whereas the same display condition might deteriorate a dye print in just weeks. Another perspective to keep in mind is that museums display at 50 Lux or lower and although much dimmer than a safe display condition of 120 Lux, it is more than adequate for viewing artwork. Galleries, because they are trying to sell work, almost always display artwork in an unsafe level of illumination. They are terrible examples to follow if you wish to preserve the artwork you purchase from them.

Longevity Testing

How long a print lasts is the subject of much controversy. OEM’s boast significantly high numbers. Most OEM ink and media users believe that their prints will not fade for 100 years if the OEM claims that a specific ink/media combination has a longevity rating of 100 years. However, that is simply not what the OEM is actually reporting. What they are reporting is that at 100 years, the print will have so badly faded to a 35% loss, that anyone can easily detect the fade. The term “easily detected fade” is used to describe the endpoint that the OEMs are using for their fade ratings – and it is an industry standard endpoint.

The industry standard WIR Visually-Weighted Endpoint Criteria Set v3.0 which is used by all the major printer OEM’s to give their longevity ratings does not measure for fade in neutrals, flesh tones, near neutrals, near whites, mixed colors, saturated colors, the paper, etc. What the industry standard tests by Wilhelm do measure are simple densitometric changes in a 1.0 and 0.60 density patch each of cyan, magenta, yellow and three color black. When any one of these patches has faded about 35%, assumptions are made on all other possible colors and a longevity result in years is given for when the print will have faded about 35%.

While a research scientist at Wilhelm Imaging Research (WIR), Mark McCormick-Goodhart (Aardenburg) invented the WIR i-Star, a new test method based on CEILAB colorimetry for evaluating the permanency of photographic images. The WIR i-Star uses a complex color target that is measured with a color spectrophotometer rather than with a densitometer.

The WIR v3.0 standard test target on the left, the WIR i-Star test target on the right.

The WIR i-Star is the most advanced method for evaluating the light stability of inks and making longevity predictions. Some of the other benefits of using WIR i-Star are that fade results for the first time can be compared in prints that use different ICC profiles (yes it makes a difference), or from cartridges that are in different stages of nearing exhaustion (yes it makes a difference), or to determine when the OBAs in a paper will affect the color appearance of an image (yes it makes a difference). Most importantly, the i-Star can be used to determine when fade will first be visible (about 5%), or/and when it has reached 35% fade, or/and many intervals in between.

Unfortunately, the OEMs are still not using WIR i-Star for their current longevity ratings. There is no way to know if that is by choice, request, the expense of performing i-Star, or because an i-Star would reveal fade levels far below the industry standard 35% and upset consumer expectations that have been established.

IMHO, replacing the current density based CMY testing method and target of WIR v3.0 with the color and luminosity based WIR i-Star target and measurement method but keeping the 35% fade point would be a great interim move by the OEMs. They could then give a fade rating based upon fade that can first be detected (about 5%) by visually trained humans and a second rating based upon when it is easily detected by any human (35%). An OEM longevity rating might be something like 13 – 120 years. It would force more of the responsibility on the consumer to read the actual data. The i-Star is also designed to give varying lengths of longevity in varying display conditions. The consumer looks up their needs within the data and has a clear idea of a display prediction for their display condition. Further, if they bias their needs on portraits, or black & white made with color inks, or very saturated color they will find that some media/ink combinations actually have better or worse results in these areas. It is as perfect a system as it is complicated.

Our experience

Vermont PhotoInkjet began utilizing the Wilhelm Imaging Research WIR i-Star beta several years ago. By using i-Star, we are able to effectively evaluate what changes to individual color positions will do to the overall light stability of an ink set as it relates to the entire color gamut of a print. It actually helped us to develop our second release of a dye ink set InkThrift CL.

We use the i-Star to make longevity predictions based upon the industry standard “easily recognizable fade” of 20% – 35%. We fade samples in 10 Megalux doses and take color spectro measurements. We continue giving 10 Megalux doses to the samples until the a 35% fade is recorded in at least 3 of the 30 patches. At that point, we consider the sample to have reached its endpoint regardless of how well the other 27 patches have done. We now use a late generation Atlas accelerated testing chamber that is filtered to simulate sunlight through window glass. The unit is temperature controlled (stays cool inside while generating tons of heat which we vent outside). The amount of light energy the targets receive is measured and controlled by a computer to compensate for fluctuations due to either electrical load or bulb decay. We use an automated x-Rite DTP70 measuring system. The DeltaE differences are calculated using X-Rite Measure Tool which compares faded targets to targets kept in safe dark storage.

The three following i-Star visual measurement sets are for InkThrift PRO and the newly released InkThrift CL ink sets. Two of the tests are conducted within the same time period (38 years at 120 Lux) reveal the superiority of CL (test II interim) over PRO (test I endpoint). Where Pro has faded to 22%-35%, the CL ink set is averaging only 12%-16%. Test III endpoint is of CL allowed to fade to about 24%-32%%. It reveals a much longer display life (up to 95 years at 120 Lux) to reach what PRO reaches in just 30 years at 120 Lux).

Below are InkThrift CL longevity expectations* in regards to varying levels of illumination (lux) at 12 hours per day from safe display conditions to extremely abusive display conditions:

The recommended safe level for displaying color dye photographs is 120 lux, 12 hour per day

for a life of up to 95 years

A brightly lit interior room at 250 lux reduces the life expectancy

up to 45 years until 35% fade

A very brightly lit room for color critical work, or for writing at 500 lux reduces the life expectancy

up to 22 years at 35% fade

A room that is brightly lit for task work, or for studying at 1000 lux reduces the life expectancy

up to 3.5 years at 35%

A commercial gallery at 2000lux reduces the life expectancy

up to 11 years until 35% fade

An interior room in which sunlight filters in through windows but does not directly strike the print at 5,000 lux reduces the life expectancy

up to 2 years at 35% fade

Direct sunlight through a window allowed to strike the print in a room at 10,000 lux reduces the life expectancy

up to 1 year

Increasing the exposure from 12 hours or decreasing the exposure from 12 hours can increase or decrease display life.

All of the above are indoor environments. Some inkjet printer operators may consider any of these environments to be the same because they are all indoors. However, the intensity of the light is directly proportional to the amount of fade. Time is the constant. 35% fade is the current industry standard endpoint used by all OEMs testing at WIR and indicate "easily recognizable fade". A 100 year rating from EPSON is for when the ink/media combination will have faded 35%.

Actual print stability will vary according to image, display conditions, light intensity, ICC profile, RIP or driver settings, humidity, and atmospheric conditions. Vermont PhotoInkjet, LLC and InkjetMall do not guarantee longevity of prints. Ratings do not estimate the durability of the media or paper itself. For maximum print life, display all prints under glass or properly store them in archival conditions, use uncoated acid-free and lignin-free paper for best practices.